The present invention relates to a novel process for converting perylene-3,4:9,10-tetracarboximides of the general formula I (referred to hereinbelow as “perylimides I” for short)
in which R1 and R2 are each unbranched, branched or cyclic C1-C8-alkyl, to a form suitable for use as fluorescent dyes.
The invention also relates to crystalline solvates of the perylimides I which contain 1 or 2 mol of solvent per mole of perylimide I.
The invention further relates to different crystalline forms of N,N′-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarboximide which are characterized by X-ray powder diagrams (CuKα) having significant lines at the following d values:
Form A (“perylimide A”): 10.2, 9.60, 8.17, 7.60, 7.07, 6.89, 6.02, 5.64, 4.89, 4.79, 4.63, 3.93, 3.81, 3.53 and 3.43 Å;
Form B (“perylimide B”): 15.3, 7.68, 7.32, 7.15, 5.99, 5.59, 5.33, 4.98, 4.24, 3.86 and 3.235 Å;
Form C (“perylimide C”): 10.67, 9.88, 9.36, 7.82, 7.16, 6.89, 5.74, 5.49, 4.68, 4.085, 3.354 and 3.252 Å;
Form D (“perylimide D”): 9.7, 8.6, 7.85, 6.88, 4.83, 4.13 and 3.81 Å;
Form E (“perylimide E”): 15.2, 14.7, 8.04, 7.76, 7.36, 6.43, 5.59, 4.99, 4.25, 4.14 and 3.863 Å.
The invention relates not least to the use of the perylimides I and the perylimides A to E prepared according to the invention as fluorescent dyes for coloring organic and inorganic polymeric materials, and also as emitter materials in electrooptical components.
EP-A-55 363 describes various perylimides which are substituted on both imide nitrogen atoms by alkyl- or chlorine-substituted phenyl, including N,N′-bis(2,6-diisopropylphenyl)perylimide.
These perylimides are prepared by reacting perylene-3,4:9,10-tetracarboxylic dianhydride with the correspondingly substituted aniline in the presence of a zinc compound and sometimes also of acetic acid as a catalyst in quinoline. The perylimides are then precipitated by adding methanol, filtered off and washed with methanol and water. To remove unconverted perylene-3,4:9,10-tetracarboxylic dianhydride, the perylimides isolated in this way are usually then stirred in hot carbonate solution.
EP-A-55 363 proposes a further variant for isolating the perylimides in which the entire reaction mixture is initially brought into solution by adding a solvent which dissolves the perylimide, such as N-methylpyrrolidone, dimethylacetamide or dimethylformamide, and heating, the solution is filtered and the perylimide is precipitated out again by adding lower alcohols, such as methanol, optionally in a mixture with water. The perylimides should usually be obtained in a sufficiently pure form.
However, according to in-house investigations, this method of precipitation results only in products of insufficient purity being obtained which contain by-products, in particular N-substituted perylene-3,4-dicarboximide, in relatively large amounts (generally >10%), and are substantially X-ray-amorphous, and also finely crystalline and difficult to filter.
For further purification, EP-A-55 363 proposes reprecipitation from sulfuric acid and also recrystallization, without giving any further information.
It is an object of the present invention to provide a process which makes it possible to efficiently purify perylimides I and in which the perylimides I are obtained directly in a form suitable for use as fluorescent dyes.
We have found that this object is achieved by a process for converting perylene-3,4:9,10-tetracarboximides of the general formula I
in which R1 and R2 are each unbranched, branched or cyclic C1-C8-alkyl to a form suitable for use as fluorescent dyes, which comprises    a) dissolving or suspending the perylene-3,4:9,10-tetracarboximides whose molecules have a molecular volume of 230 Å3 in an organic or inorganic solvent at from 0 to 250° C.,    b1) cooling the solution obtained in step a) to or below the crystallization temperature and, in the case of an organic solvent, if desired at the same time removing excess solvent until the first crystals form, or, in the case of an inorganic solvent, adding water or dilute aqueous solutions of the solvent until the first crystals form, and maintaining the solution at this temperature for further crystallization or    b2) cooling the suspension obtained in step a) to or below the crystallization temperature when the temperature in step a) was above the crystallization temperature, and maintaining the suspension at this temperature for further crystallization,    c) isolating the solvate crystals formed in step b) and    d) then removing the solvent from the solvate crystals.
It is essential to the process according to the invention that the solvent molecules used in step a) have a molecular volume of
≦230 Å3, preferably ≦200 Å3 and more preferably ≦180 Å3, and are therefore able to form stable binary crystal phases (solvates or else clathrates) with the perylimide I which contain up to 2 molecules of solvent per molecule of perylimide I.
The molecular volumes specified may be calculated from the structure of the molecule by the method published by Gavezzotti (J. Amer. Chem. Soc. 1989, 11, p. 1835).
Preference is given to using solvents in which the perylimide I dissolves, optionally after heating, although solvents may also be used in which the perylimide I only partially dissolves at the treatment temperature. The conversion to the corresponding solvates is then effected in suspension.
Accordingly, useful organic solvents are in particular (the term alkyl is also intended to encompass cycloalkyl, in particular cyclohexyl):                di-C1-C4-alkylsulfoxides, such as dimethyl sulfoxide;        sulfolane;        unsubstituted and N—C1-C6-alkyl-substituted C4-C6-lactams, such as pyrrolidone, N-methylpyrrolidone, N-cyclohexylpyrrolidone, N-octylpyrrolidone, caprolactam and N-ethylcaprolactam;        unsubstituted and N—C1-C6-alkyl-substituted aliphatic C1-C6-carboxamides, such as formamide, dimethylformamide, dimethylacetamide, benzamide and N-acetylmorpholine;        aliphatic nitriles having from 2 to 12 carbon atoms, such as acetonitrile and 2-methoxypropionitrile;        aromatic nitriles which may be substituted by C1-C8-alkyl, C1-C8-alkoxy and/or halogen, such as benzonitrile and 3-methylbenzonitrile;        aliphatic C1-C12-carboxylic acids and their C1-C6-alkyl esters having a total number of carbon atoms of ≦12, such as formic acid, acetic acid, propionic acid, 2-ethylhexanoic acid and ethyl acetate;        hydroxy-C2-C6-carboxylic acids and their esters, such as lactic acid, butyrolactone, valerolactone and caprolactone;        C2-C6-alkylene carbonates, such as ethylene carbonate and propylene carbonate;        benzoic acids, such as benzoic acid, phthalic acid and terephthalic acid;        naphthoic acids, such as α- and β-naphthoic acid;        C1-C6-alkyl benzoates, such as methyl benzoate and ethyl 3-methylbenzoate;        di-C1-C2-alkyl phthalates, such as diethyl phthalate;        monohydric and polyhydric, saturated and unsaturated, aliphatic and cycloaliphatic C4-C12-alcohols, such as butanol, isoamyl alcohol, cyclohexanol, octanol, 3-methyl-1-pentyn-3-ol, methoxypropanol, furfuryl alcohol, tetrahydrofurfuryl alcohol and 1,5-pentanediol; araliphatic alcohols, such as benzyl alcohol, 2-phenylethanol and 4-methoxybenzyl alcohol;        mono- and oligo-C2-C3-alkylene glycol mono- and -di-C1-C8-alkyl- and monophenyl ethers, such as ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether and diethylene glycol dimethyl ether;        aliphatic C3-C12-ketones, such as acetone, methyl isobutyl ketone, diacetone alcohol, cyclohexanone and 2-methylcyclohexanone;        aromatic ketones which may be substituted by C1-C8-alkyl, C1-C8-alkoxy and/or halogen, such as isophorone, acetophenone, propiophenone, 3-chloroacetophenone and 3-ethylacetophenone;        aliphatic and cycloaliphatic C4-C12-ethers, such as methyl tert-butyl ether, ethyl isobutyl ether, 2-ethylhexyl methyl ether, tetrahydrofuran and dioxane;        aromatic ethers which may be substituted by C1-C8-alkyl, C1-C8-alkoxy and/or halogen, such as diphenyl ether;        heterocycles, such as pyridine, picoline, lutidine, quinoline, methylquinoline, imidazole, methylimidazole and 1,3-dimethyl-2-imidazolidinone;        aromatic hydrocarbons which may be substituted by C1-C8-alkyl, C1-C8-alkoxy, C1-C6-alkylamino, di-C1-C3-alkylamino, chlorine and/or nitro, such as toluene, o-, m- and p-xylene, ethylbenzene, cumene, methoxybenzene, chlorobenzene, o-dichlorobenzene, 1,2,4-trichlorobenzene, nitrobenzene, phenol, 3-methylphenol, p-chlorophenol, o-nitrophenol, N-hydroxyethylaniline, 1,2,3,4-tetrahydronaphthalene, 2-chloronaphthalene, 2-methoxynaphthalene and dimethylnaphthalene;        aliphatic and cycloaliphatic C6-C18-hydrocarbons, such as limonene, decalin and methylcyclohexane;        chlorohydrocarbons, such as methylene chloride, chloroform, tetrachloromethane, dichloroethane, trichloroethane and tetrachloroethane.        
It will be appreciated that mixtures of these solvents may also be used.
Preferred organic solvents are xylene, toluene, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, methyl isobutyl ketone, methylene chloride, ethylene glycol monophenyl ether and ethylene glycol monobutyl ether.
It is also possible to use combinations of these solvents, i.e. to initially form a solvate with a first solvent (for example N-methylpyrrolidone) and to exchange the solvent in this solvate by treating with a second solvent (for example acetic acid).
Useful inorganic solvents are in particular acids, in particular sulfuric acid.
In step a) of the process according to the invention, the perylimide I is either dissolved in the solvent or suspended therein.
Accordingly, when organic solvents are used, the procedure in accordance with the invention may be as follows: a mixture of perylimide I and solvent is heated to a temperature at which the perylimide I dissolves in the solvent, the resulting solution is then cooled in step b1) to or below the crystallization temperature of the perylimide I and the solution is maintained at this temperature for further crystallization; the crystallization may, if desired, be promoted by at the same time removing excess solvent. Or the perylimide I is suspended in the solvent, preferably at elevated temperature, to increase the purifying effect, the resulting suspension is then cooled in step b2) to or below the temperature at which the solvate crystals crystallize out and the suspension is maintained at this temperature for further crystallization.
When inorganic solvents are used, the procedure may similarly be as follows: the perylimide I is dissolved at a suitable temperature in substantially anhydrous to highly concentrated solvent and the crystallization is initiated in step b1) by diluting the solvent with water or aqueous solutions of the solvent. Or the perylimide I is stirred directly for several hours in a less concentrated solvent, preferably at temperatures around room temperature, likewise resulting in the formation of solvate crystals.
This will now be illustrated in detail using the example of the particularly preferred solvent sulfuric acid. In the first variant, it is advisable to dissolve the perylimide I at approximately room temperature (approx. 20-30° C.) in about 96 to 100% by weight sulfuric acid, then to gradually reduce the sulfuric acid concentration by adding water or more dilute sulfuric acid (for example 20% by weight sulfuric acid) to about 70 to 93% by weight and thus effect the crystallization of a sulfate of the perylimide I. In the second variant, about 70 to 90% by weight sulfuric acid is used directly.
Depending on the molecular size of the solvent, the crystalline solvates which are obtained in step c) of the process according to the invention and are likewise according to the invention have a molar composition of solvent to perylimide I of 1:1 (for example in the case of xylene, N-methylpyrrolidone, methoxybenzene and dimethylacetamide solvates) or 2:1 (for example in the case of methylene chloride and acetic acid solvates). Despite the same gross composition, the crystalline phases may have different crystal structures. In the case of some of these solvates (for example in the case of methylene chloride and acetic acid solvates), the solvent molecules may leave the perylimide host lattice without its crystalline structure changing significantly. In such cases, nonstoichiometric binary phases of solvent and perylimide I may also be formed.
The exact composition of the sulfuric acid solvates generally cannot be determined, since the solvates rapidly lose sulfuric acid when isolated. However, characterization by X-ray powder diffractometry is just as possible as in the case of the solvates with organic solvents.
The solvent is then removed from the solvate crystals in step d), resulting substantially in the retention of the crystalline structures formed in step b) or else the formation of new crystalline phases. The solvent is advantageously removed by drying solvate crystals, optionally under reduced pressure and at elevated temperature. If desired, the solvate crystals may have been additionally treated (washed) before drying, with a solvent which itself does not form a solvate, preferably with water or mixtures of organic solvents with water.
The crystalline forms of the perylimides I obtained according to the invention may be characterized by X-ray powder diffractometry or by single crystal structural analysis. This resulted in the crystalline perylimides A to E which are likewise according to the invention being found, which are obtainable by crystallization from methylene chloride (perylimide A), acetic acid (perylimide B), sulfuric acid (perylimides C and D) and M-methylpyrrolidone/acetic acid (perylimide E). The X-ray powder diagrams of these perylimides are depicted in FIGS. 1 and 3 to 6.
The process according to the invention has a series of advantages which could not have been predicted. For instance, not only was it made easier to crystallize the perylimides I, but coarsely crystalline crystals were also formed which are easy to filter, can be washed without significant product loss and additionally have high purities of generally >90% (by-products formed in the synthesis such as N-monoalkylation products can be removed without any problem). The use of sulfuric acid as solvent generally allows the degree of purity to be further increased to >95% by additional removal of decarboxylation products occurring in the synthesis, so that, irrespective of the way in which the crude materials I used are synthesized, product qualities can be obtained in a simple manner which are otherwise only obtainable by chromatography. The crystals formed are notable not least for their high dissolution rates which allow them to be particularly readily incorporated into plastics.
Accordingly, the perylimides I obtained according to the invention, in particular the perylimides A to E, have outstanding suitability as fluorescent dyes for coloring organic and inorganic polymeric materials and also as emitter materials in electrooptical components, for example displays and emissive color filters, for which the perylimide A in particular is suitable owing to its marked solid state fluorescence.